The invention relates to reliable communications of data by supplementing a unidirectional communications protocol.
With improvements in communications technology, it has become possible to transport data along with television content. Traditionally, such data included ancillary information such as program sub-titles, emergency messages, closed caption messages, and program guide information. However, more recently, other types of ancillary information that may be sent with television content include enhancement data such as web pages, multimedia information, or other digital data files.
Various standards exist that provide for transmission of ancillary information along with television content. One standard is the Advanced Television Enhancement Forum (ATVEF) Specification, Draft Version 1.1r26, dated Feb. 2, 1999. The ATVEF Specification is designed to provide for transmission of enhancement data along with television content in both analog and digital systems, such as cable systems, satellite systems, terrestrial systems, and so forth.
The ATVEF Specification utilizes a one-way transmission protocol, the Unidirectional Hypertext Transfer Protocol (UHTTP), as described in the ATVEF Specification, to deliver portions of television enhancement data. UHTTP defines a one-way multicast-based data transfer protocol. However, the one-way transfer of enhancement data as defined by UHTTP does not provide a mechanism to send messages back to a source to request resends. UHTTP does provide for the ability to fill in missing segments of enhancement data by sending data repeatedly. A device at the receiving end is able to fill in missing segments of data using the retransmitted files. However, if the total amount of enhancement data is large, the time needed to transfer an entire cycle of enhancement data may be large, perhaps as much as several hours, for example. Thus a receiver may have to wait a large amount of time before missing segments of data are retransmitted again. In a purely one way protocol there is no way to know how many times data must be sent to be sure of delivery.
UHTTP also provides a forward-error correction (FEC) scheme that enables recovery of some types of missing data. However, the amount of data that may be recovered using FEC may be limited.
A need thus exists for a more reliable method and system for communicating ancillary information built on top of a unidirectional communications protocol.
In general, according to one embodiment, a system for receiving data over a link includes a receiver to receive data communicated according to a one-way communications protocol. A controller processes the received data to determine if a portion of expected data is missing. The controller is able to generate a request for the missing data.
Other features and embodiments will become apparent from the following description and from the claims.